1. Field of the Invention
The present invention relates generally to wireless communications systems, and more particularly to channel power control in a fixed multi-line wireless terminal.
2. Description of Related Art
In many parts of the world, it is expensive or difficult to run copper wire or fiber optic cable to homes and businesses to provide local phone service. A wireless local loop telephone system enables service providers to service such areas without the need for cable and its associated costs.
In a wireless local loop system, telephones and other terminal equipment at a customer site are connected to a fixed wireless terminal (FWT). The fixed wireless terminal communicates with the public switched telephone network (PSTN) through a wireless radio link, thereby enabling basic telephone service to be provided to customers who would not otherwise have access to telecommunications services, at a fraction of the cost of a traditional wire line infrastructure. Because wireless local loop systems provide telecommunications system operators with the benefits of rapid deployment, large coverage area, large capacity, and lower operating and maintenance costs, digital wireless telephone networks may be deployed rapidly and economically in developing countries which lack sufficient land-line infrastructure.
In a multi-line fixed wireless terminal, multiple channel units share a common transmitter. The transmitter controls the transmit power of each channel unit based on power level commands received from the base station(s) servicing the FWT. More specifically, each individual channel unit provides the transmitter with a set of baseband I land Q modulation signals, as well as a power control signal to control the attenuation of the transmit power level of each individual channel unit.
Adjusting the power levels of the respective channel units in a multi-line FWT is problematic. One possible way to independently adjust the transmit power of each individual channel unit requires performing all power adjustments at baseband prior to combining the individual transmit baseband channels. However, with such an approach, if all individual channel units were requested to reduce their power to a minimum level, the signal to noise ratio would be reduced to unacceptably low levels.